Microcystin producing cyanobacterial communities in Amvrakikos Gulf (Mediterranean Sea, NW Greece) and toxin accumulation in mussels (Mytilus galloprovincialis)

Abstract

Various cyanobacterial species have the capacity to produce different types of toxins. Microcystins, the most prominent cyanotoxins are considered health hazards because of their potential hepatotoxic effects. They are well known to contaminate freshwater ecosystems but their presence in marine ecosystems has been reported only occasionally. We investigated seasonal changes of microcystin concentrations both in water and in the edible species of mussels Mytilus galloprovincialis collected from Amvrakikos Gulf (salinity ranging from 30‰ to 34‰), the biggest semi-enclosed basin in Greece. The microcystin concentrations in the water ranging from 0.003 to 19.8ngl−1, were below the World Health Organization (WHO) upper limit for recreational activities. In contrast, we found that microcystin concentrations in M. galloprovincialis mussels (ranging from 45±2 to 141.5±13.5ngg−1ww) exceeded the upper limit of the tolerable daily intake (TDI) of microcystin as determined by WHO.Genotype composition of the total cyanobacterial community of the Gulf was analyzed by using denaturing gradient gel electrophoresis (DGGE) profiling of the rRNA internal transcribed spacer region (rRNA-ITS). The cyanobacterial community was found to be dominated almost exclusively by the cosmopolitan species Synechococcus –Synechocystis. In order to determine genes involved in the production of microcystins, a range of both specific and degenerate molecular primers against microcystin synthetase gene cluster (mcyS) was used.To our knowledge this is the first report of the presence of the hepatotoxic microcystins in the Mediterranean Sea, the first study on the accumulation of these toxins in mussels from a Mediterranean marine ecosystem and one of the few published works suggesting a potential association of microcystins with Synechococcus and/or Synechocystis cyanobacteria.The importance of our study is strengthened by the fact that Amvrakikos Gulf is among the most productive Greek “seafood” areas and a Mediterranean wetland of international significance according to Ramsar Convention.